Title

Author

Date of Award

Degree Type

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Alpas, Ahmet (Mechanical, Automotive and Materials Engineering)

Keywords

Materials Science.

Rights

CC BY-NC-ND 4.0

Abstract

The use of minimum quantity lubrication (MQL) machining, i.e. drilling and tapping of aluminum and magnesium alloys using very low quantities of cutting fluids was studied and the MQL machining performance was compared to dry and conventional flooded conditions. An experimental drilling station with an MQL system was built to measure torque and thrust force responses. Uncoated and diamond- like carbon (DLC) coated HSS drills were tested against 319 Al and AZ91 alloys using 10-50 ml/h of distilled water (H2O-MQL) and a fatty acid based MQL agent (FA-MQL). The results indicated that H2O-MQL used in conjunction with non-hydrogenated DLC (NH-DLC) coatings reduced the average torque and thrust-force compared to dry cutting and achieved a performance comparable with conventional flooded drilling. At least 103 holes could be drilled using NH-DLC in H2O-MQL and uncoated HSS in FAMQL in drilling of both 319 Al and AZ91. MQL drilling and tapping provided a stable machining performance, which was evident from the uniform torque and force patterns and also resulted in desirable hole surface, thread quality and chip segments. The maximum temperature generated in the workpiece during MQL machining was lower than that observed in dry drilling and tapping, and comparable to flooded conditions. The mechanical properties of the material adjacent to drilled holes, as evaluated through plastic strain and hardness measurements, revealed a notable softening in case of dry drilling, with magnesium alloys exhibiting a recrystallized grain zone, but not for MQL drilling. Softened aluminum and magnesium promoted adhesion to the tools resulted built-up edge formation and consequently high torques and thrust-forces were generated. NH-DLC coatings low COF in H2O-MQL against 319 Al (0.10) and AZ91 (0.12) compared to uncoated HSS (0.63 and 0.65) limited the temperature increase during NHDLC in H2O-MQL drilling and hence both torques and thrust forces were effectively reduced.